If you don't acknowledge your mistakes, you will keep making them.
Sherman is on record as stating he made a similar offer to the Seahawks and they turned him down. So clearly someone did not want him on the team. Did they let him go because he was a PIA?
The thing is, if you want to win - you sometimes need to deal with it. You will have people you don't like, if not cannot stand, because they produce on the field.
(Talk to the 49ers about Charles Haley, the stories of all the horrible things he did almost stretch belief - stories of him jerking off in front of players' wives and gfs, peeing on the desks/lockers, etc. Most are probably more legend than truth, but they apparently shipped him off because he was a PIA.
Interestingly enough, he ended up in Dallas...SF's rival. And Dallas won multiple SBs, instead of SF - because Dallas edged out SF repeatedly. Haley was a big part of that. SF did not get to another SB, until much later. Haley wasn't the whole reason, but SF took a while to live down letting go of Haley until the 49ers built what was pretty much an All-Star team back in 95.)
Now we released Sherman, let him go to our rival, he immediately shores up one of the bigger weaknesses for the 49ers (secondary) and they end up in the SB instead of us.
Our coaches should have put winning ahead of their personal preferences.
We had nobody to even replace him. Keeping Sherman was risky, but not nearly at the #s he was offering since most would be production-based. It didn't need to be 20-20 hindsight because there was plenty of upside in keeping him and not a ton of downside, other than some people on our coaching staff getting their feelings hurt. Again, with nobody to replace him - we left ourselves with a big hole.
Our coaches' likely worry about their feelings strengthened a rival and contributed to that rival making a SB vs us even finally being effective in a divisional playoff game in almost half a decade. Can you call that anything BUT a yawning mistake?